You can snipe several auctions from anyone (including the same seller) in a bid group. They just can't end only seconds apart. 25-30 seconds or more should work fine for you as long as you keep your lead time under about 10 seconds.
If you are talking about different items (not in a bid group) that end at the same time... Again yes, you can do that too. Just enter them in My Snipes or another folder that is NOT a bid group.
Of course as BullBar said, you can't make a 'conditional' snipe... not yet anyway.
WELCOME !